In this application, we propose to be one of 20 clinical centers selected to participate in a collaborative clinical trial on the relationship between blood glucose control and vascular complications in patients with insulin-dependent diabetes mellitus. After development of a final protocol with other clinical centers and the NIAMDD staff, we will randomize 10 insulin-dependent diabetic patients between the ages of 10 and 28 to conventional therapy with diet, exercise, and split doses of insulin or to an intensive therapy regimen. These latter patients will be carefully instructed and followed so that precise metabolic control of diabetes can be achieved by portable insulin pump and/or frequent injections of insulin. All patients will be initially hospitalized for baseline studies, psychological testing, education and adjustment of therapy on the General Clinical Research Center. Major end points to be followed will be optic fundus photography and nerve conduction times. Vascular indices to be followed will include urinary protein, lipids and lipoproteins, platelet function, prostacyclin metabolism of platelets and endothelium, kallikrein and kinins. Patients will have HLA typing, organ-specific antibodies and immune complexes determined. It is expected that over the two year period of this feasibility study that it can be determined if a strict control regimen is feasible and has high degree of patient acceptability. Further, it should be possible to establish methods for assessing and monitoring metabolic control and enpoints of pathologic complications which can be used in a subsequent full-scale clinical trial.